Electrical cable coupler



Nov. 24, 1959 l. s. BLONDER ELECTRICAL CABLE COUPLER Filed Feb. 16, 1955INVENTOR. ISAAC S. BLONDER ATTORNEYS United States Patent ELECTRICALCABLE COUPLER Isaac S. Blonder, Roselle, NJ.

Application February 16, 1955, Serial No. 488,660

6 Claims. (Cl. 333-97) The present invention relates to electrical cablecouplers and, more particularly, to radio-frequency coaxialtransmission-line couplers.

Standard types of male connectors have been established in the art foruse with coaxial transmission lines such as, for example, theconventional 75-ohm coaxial cable widely utilized in television andother radio-frequency systems. Frequently, it is required that twosections of cable, each having such a male connector, be electricallyand mechani cally joined together. Couplers or splicer-junctions havebeen proposed for accomplishing this purpose, but, unfortunately, suchcouplers have been found to introduce impedance discontinuities at thejunction of the coaxial-line sections. As an illustration, many of suchcoaxial-cable couplers have impedances that are only of the order ofabout 25 ohms. When these couplers are utilized to join two sections of,for example, the before-mentioned 75- ohm coaxial cable, a seriousimpedance mismatch or discontinuity is produced, resulting in theproduction of deleterious standing waves. This is not too serious aproblem, however, in the event that the junction of the coaxial cablesis to be effected at or in the electrical equipment associated with thecables. This is because compensation for such impedance discontinuitiescan be introduced in the circuits of that equipment. When, however, itis necessary to splice coaxial cables at a point remote from the.equipment, or to pass the cables through a metal or other wall, withthe requirement that the shield or outer conductor of the cable begrounded at the point of connection, this impedance discontinuityproblem becomes of considerable significance. Serious impedancemis-matches and standing-wave phenomena result that do not lendthemselves to easy compensation.

An object of the present invention, therefore, is to provide a new andimproved electrical-cable coupler that shall not be subject to thebefore-mentioned difilculties and that, on the contrary, is particularlysuited for the joining together of electrical cables at points remotefrom their associated electrical equipment.

Another object is to provide a new and improved radiofrequencycoaxial-line-cable coupler.

.Other and further objects will be explained hereinafter and will bemore particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanyingdrawings, Fig. l of which is a perspective view illustrating theinvention in preferred form, with the parts being shown dis-assembledand partly broken away, in order to illustrate the details ofconstruction; and

Fig. 2 is a side elevation, partly in section, illustrating the parts,as assembled.

Conventional present day coaxial-line male connectors are shown at 1 and3 provided with respective outer cylindrical conductors 2 and 5 andinner-conductor plugs 4 and 7. The plugs 4 and 7 are usually mounted ininsulating separators, such as the insulation disc 6 associated with theconnector 1, coaxially disposed within the outer conductors. Conductivecollars or sleeves 8 and 9 are ICC disposed about the respective outerconductors 2 and 5 and are free to move thereon within predeterminedlimits. The interior surfaces of the collars 8 and 9 are threaded, asshown at 10 and 11, for cooperating with the threads of a female-typecoaxial connector, not shown, with which they are usually employed. Thethreaded collars 8 and 9 are limited in their movement coaxially overthe respective outer conductors 2 and 5 of the coaxial-line connectors 1and 3 by flanges 20 and 13 upon the respective outer conductors 2 and 5.

The connectors 1 and 3 are shown associated with respective coaxial-linesections 12 and 12' which are to be joined together electrically andmechanically. Referring to the coaxial-line section 12, for example, itsinsulationcovered outer sheath conductor 14 is separated by insulation16 from the inner conductor 18. The outer sheath conductor 14 makeselectrical contact with the outer connector conductor 2 and the innerconductor 18 makes electrical contact with the connector plug 4, as iswell known. In similar fashion, the outer conductor 14' of thecoaxial-line section 12 is connected to the outer conductor 5 of theconnector 3 and the inner conductor 18 is connected to the inner plugconductor 7.

In accordance with the present invention, the two male connectors 1 and3 are coupled together by an externally threaded conductive tube 22. Theexternal diameter of the tube 22 and the threads thereupon are such thatthe collars or sleeves 8 and 9 of the respective connectors 1 and 3 maybe threaded upon opposite ends of the tube. In this manner, the collars8 and 9 of the respective connectors 1 and 3 may be joined togetherelectrically and mechanically. When threaded to a sufficient degree uponthe conductive tube 22, moreover, the collars 8 and 9 will respectivelycontact the before-mentioned flanges 20 and 13 of the outer conductors 2and 5 of the respective coaxial-line conductors 1 and 3, thereby toestablish electrical connection between the outer conductors 14 and 14'of the respective coaxial-line sections 12 and 12. The degree ofthreading may be limited by adjustable stop washers 29, permitting theuse of the invention with connectors of different lengths, andpermitting easy attachment to the before-mentioned metal or other walls.

Electrical connection between the inner conductors 18 and 18 of thecoaxial-line sections 12 and 12 is established through the medium of apreferably helical spring member 24 of cross dimension or diametersomewhat larger than the cross-dimension or diameter of theinner-conductor plugs 4 and 7. The spring 24 receives the plugs 4 and 7at opposite ends. The terminal portions of the helical spring arepreferably soldered together to provide continuous conductiveterminal-portion sheaths 26 and 27 for reasons later explained. Thelength of the terminal portions 26 and 27 is substantially equal to andpreferably somewhat greater than the length of the inner conductor plugs4 and 7, and the overall length of the helical spring member 24 issomewhat greater than the overall length of the tubular member 22.Interconnecting the terminal portions 26 and 27 of the helical springmember 24 is an intermediate portion constituted of several spacedresilient turns of the spring, as shown at 28.

When the collars 8 and 9 of the male connectors 1 and 3 are threadedupon the tube 22 to the appropriate degree, as before stated, thusproviding electrical contact between the outer conductors 14 and 14 ofthe respective coaxial-line sections 12 and 12, the spring member 24 iscompressed between the conductive collars 30 and 31 at the inner ends ofthe respective plugs 4 and 7. No further support for the spring member24 is needed, since this is furnished by the plugs 4 and 7 of the maleconnectors 1 and 3.

The structure as thus far described provides an excellent electrical andmechanical coupling between the coaxial-line sections 12 and 12. It isnecessary, however, also to solve the problem of avoiding thedeleterious effects, before mentioned, of impedance discontinuitiesresulting from an impedance mismatch between the connectors 1 and 3 andthe coupler 22, 24. The connectors 1 and 3 inherently have a highercapacity between their inner and outer conductors than exists along thecoaxial transmission line iteself. This must be compensated for at thecoupling between the connectors if impedance discontinuities are to beavoided. In accordance with the present invention, such substantialimpedance discontinuities are avoided through proper dimensioning of thecoupling member 24 in order to provided an increased series inductancein the center conductor formed by the coupled plugs 4 and 7 that shallcompensate for the higher capacity of the connectors 1 and 3. As beforeindicated, sufficient turns are present in the intermediate portion 28of the spring member 24 to provide adequate resiliency for mechanicaland electrical connection between the inner-conductor plugs 4 and 7. Oneof the reasons for providing continuous terminal portions 26 and 27,indeed, resides in the fact that the resiliency is then limited to theregion between the plugs 4 and 7, thus insuring a more satisfactoryspring action than if the complete member 24 were resilient. Bysimultaneously selecting the appropriate diameter of the turns 28 andthe appropriate number of turns, however, a predetermined amount ofseries inductance may be introduced in the series connection between theinner plug conductors 4 and 7. This series inductance may be made of thenecessary value to compensate for the before-mentioned high capacity ofthe connectors 1 and 3, thus to match the impedance of the coupledconnectors 1 and 3 to that of the lines 12 and 12. Since the inductancecontributed by the spring member 24 is the sum of the inductances of theterminal portions 26 and 27 and the inductance of the intermediate turns28, it is important to reduce the inductance contribution at theterminal portions 26 and 27 in view of the fact that inductance isalready contributed at the regions occupied by the terminal portions 26and 27 by the plugs 4 and 7. This is another reason for rendering theterminal portions 26 and 27 continuous, so that they present a smallinductance compared with that provided by the intermediate turns 23. Itis then easy to efiect the insertion of the necessary compensatingseries inductance merely through the design of the intermediate turns28.

As a typical illustration, where conventional 75-ohrn coaxial lineconnectors l and 3 are utilized having inner conductor plugs 4 and 7about an eighth of an inch in diameter extending about three-eighths ofan inch coaxially within the collars 8 and 9 from the insulatingsupports 6 and 5, the interiorly threaded collars 8 and 9 arecustomarily about A of an inch in diameter. An appropriate conductivetube 22 having the same thread pitch and number of threads per inch asthe threads 10 and 11 of the collars 8 and 9 may have an outer diameterof substantially /8 of an inch, an inner diameter of about of an inchand a length of about 1 inches. The helical spring 24 may have an innerdiameter of about 0.175 inch and the terminal portions 26 and 27 mayeach be about of an inch in length. In order to provide not onlysufiicient resiliency but, also, the correct amount of series inductanceto compensate for the high capacitance of the coaxial-line connectors 1and 3, thereby to avoid substantial impedance discontinuity between theconnectors 1 and 3, it has been found that substantially three completeturns of 0.032 inch wire, spaced apart over a distance of substantiallyof an inch, should be provided in the intermediate region 28. It isconvenient to form the spring member 24 into the illustrated shape andthen to dip the whole spring member into solder. The close-togetherturns at the terminal portions 26 and 27 become thus soldered togetherinto low-inductance continuous conducting sheaths, whereas theintermediate turns 28 retain their spacing, serving as a relatively highinductance coil of the required predetermined value.

While the invention has been described in connection with 75-ohmconnectors, it is clear that the same underlying principles may beapplied equally to cable connectors of other impedance values and ofother configurations. If all of the features of the present inventionare not desired, other types of spring members may also be employed.

Further modifications will occur to those skilled in the art and allsuch are considered to fall within the spirit and scope of theinvention, as defined in the appended claims.

What is claimed is:

1. A coaxial-line coupler for connecting together two male coaxial-lineconnectors each having an outer conductor and an inner-conductor pluginsulated therefrom and extending coaxially within the same, the couplercomprising means for mechanically and electrically joining the outerconductors of the connectors, and a spring member of cross dimensionlarger than the cross-dimension of the plugs but smaller than thecross-dimension of the outer conductors, the spring member having twoterminal portions providing a continuous conductive sheath for receivingthe plugs of the connectors and an intermediate portion having turnsspaced apart to provide resilience for the spring member, the turns ofthe intermediate portion being adjusted to permit the spring member tobecome compressed within the outer conductors between the plugs of theconnectors when the connectors are joined together and simultaneously topresent a predetermined value of series inductance in the connectionbetween the plugs suflicient to compensate for the capacity of theconnectors in order to prevent a substantial impedance discontinuitybetween the connectors.

2. A coaxial-line coupler for connecting together two male coaxial-lineconnectors each having an interiorly threaded collar adapted to contactthe outer conductor of the connector and an inner-conductor pluginsulated therefrom and extending coaxially within the collar, thecoupler comprising an externally threaded conductive tube upon which thecollars of the connectors may be threaded for mechanically andelectrically joining the outer conductors of the connectors, and ahelical spring member of cross dimension larger than the cross-dimensionof the plugs but smaller than the cross-dimension of the conductive tubeand of length greater than the length of the tube, the spring memberhaving two terminal portions the turns of which are joined together toprovide a continuous conductive sheath for receiving the plugs of theconnectors and an intermediate portion the turns of which are spacedapart to provide resilience for the spring member, the turns of theintermediate portion being adjusted to permit the spring member tobecome compressed within the conductive tube between the plugs of theconnectors when the connectors are threaded upon the tube andsimultaneously to present a predetermined value of series inductance inthe connection between the plugs sufficient to compensate for thecapacity of the connectors in order to prevent a substantial impedancediscontinuity between the connectors.

3. A coaxial-line coupler for connecting together two male coaxial-lineconnectors each having an interiorly threaded collar adapted to contactthe outer conductor of the connector and an inner-conductor pluginsulated therefrom and extending coaxially within the collar, thecoupler comprising an externally threaded conductive tube upon which thecollars of the connectors may be threaded for mechanically andelectrically joining the outer conductors of the connectors, stopssecured to the tube to limit the position of the collars thereupon, anda helical spring member of cross-dimension larger than thecrossdimension of the plugs but smaller than the cr0ss-dirnension of theconductive tube and of length greater than the length of the tube, thespring member having two terminal portions the turns of which aresoldered together to provide a continuous conductive sheath forreceiving the plugs of the connectors and an intermediate portion theturns of which are spaced apart to provide resilience for the springmember, the turns of the intermediate portion being adjusted to permitthe spring member to become compressed within the conductive tubebetween the plugs of the connectors when the connectors are threadedupon the tube and simultaneously to present a predetermined value ofseries inductance in the connection between the plugs sufiicient tocompensate for the capacity of the connectors in order to prevent asubstantial impedance discontinuity between the connectors.

4. A 75-ohm coaxial-line coupler for connecting together two male 75-ohmcoaxial line connectors each having an interiorly threaded collarsubstantially 1 of an inch in diameter adapted to contact the outerconductor of the connector and an inner-conductor plug about Vs of aninch in diameter insulated therefrom and extending about of an inchcoaxially within the collar, the coupler comprising an externallythreaded conductive tube subrtantially /6 of an inch outer diameter, ofan inch inner diameter, and 1 inches in length, upon which the collarsof the connectors may be threaded for mechanically and electricallyjoining the outer conductors of the connectors, and a helical springmember substantially 0.175 inch inner diameter, the spring member havingtwo terminal portions each substantially of an inch long providing acontinuous conductive sheath for receiving the plugs of the connectorsand an intermediate portion having substantially three turns ofsubstantially .032 inch wire spaced apart over a distance ofsubstantially of an inch to provide series inductance in the connectionbetween the plugs sufiicient to compensate for the capacity of theconnectors in order to prevent a substantial impedance discontinuitybetween the connectors.

5. A coaxial-line coupler for connecting together two male coaxial-lineconnectors each having, an outer conductor and an inner-conductor pluginsulated therefrom and extending coaxially within the same, the couplercomprising means for mechanically and electrically joining the outerconductors of the connectors, and a spring member of cross dimensionlarger than the cross dimension of the plugs but smaller than the crossdimension of the outer conductors, the spring member having two terminalportions for receiving the plugs of the connectors and an intermediateportion having turns spaced apart to provide resilience for the springmember, the turns of the intermediate portion being adjusted to per mitthe spring member to become compressed within the outer conductorsbetween the plugs of the connectors when the connectors are joinedtogether and simultaneously to present a predetermined value of seriesinductance in the connection between the plugs sufficient to compensatefor the capacity of the connectors in order to prevent a substantialimpedance discontinuity between the connectors.

6. Apparatus of the character described comprising two male coaxial-lineconnectors each having an outer conductor and an inner-conductor pluginsulated therefrom and extending coaxially within the same providing apredetermined capacity, means for mechanically and electrically joiningthe outer conductors of the connectors, and a spring member of crossdimension larger than the cross dimension of the plugs but smaller thanthe cross dimension of the outer conductors, the spring member havingtwo terminal portions providing continuous electrically conductingsheaths for receiving the plugs of the connectors and an intermediateportion having turns spaced apart to provide resilience for the springmember, the turns of the intermediate portion being adjusted to permitthe spring member to become compressed within the outer conductorsbetween the plugs of the connectors when the connectors are joinedtogether and simultaneously to present a predetermined value of seriesinductance in the connection between the plugs suflicient to compensatefor the said predetermined capacity of the connectors in order toprevent a substantial impedance discontinuity between the connectors.

References Cited in the file of this patent UNITED STATES PATENTS1,852,190 Roe Apr. 5, 1932 2,425,834 Salisbury Aug. 19, 1947 2,449,983Devol Sept. 28, 1948 2,451,413 Robinson Oct. 12, 1948 2,716,202 LittleAug. 23, 1955 2,732,534 Giel Jan. 24, 1956 FOREIGN PATENTS 1,047,285France Dec. 14, 1953

